1. Field of the Invention
The present invention relates to a high tenacity fiber for reinforcing plastic composites and to the composites themselves wherein the reinforcing fiber, selected from the group consisting of polyester, aliphatic polyamide and combinations thereof, has been treated with a composition consisting essentially of an organo-functional silane in an amount sufficient to achieve 0.02 to 1.0 weight percent of the silane on the fiber and a diluent which provides for the hydrolysis of the silane to a silanol. More particularly, the present invention relates to a high tenacity, high elongation, low shrinkage polyester fiber which has been treated with a composition consisting essentially of water and gamma-glycidoxypropyltrimethoxysilane in an amount sufficient to achieve 0.02 to 1.0 weight percent of the silane on the fiber, especially for use in reinforcing a composite wherein the resin matrix comprises unsaturated polyester resin or other thermosetting or thermoplastic resins. The reinforcements can be used in bulk and sheet molding compounds, filament winding, pultrusion, spray-up and hand-layup.
2. The Prior Art
A composite consists of basically three major elements: the resin matrix, the reinforcement dispersed in the matrix, and the reinforcement-resin matrix interface. Synthetic fibers in staple or filamentary form, and fabrics produced therefrom, are known for polymer reinforcement. Typical of the fibrous reinforcements are glass, polyester, polyamide (nylon and aramid) and polyolefin fibers. Conventional matrix resins include thermoplastics, such as nylon and polyolefins, and thermosetting materials, such as epoxy and unsaturated polyester resins. Since the primary function of the fiber matrix interface is to transmit stress from the matrix to the reinforcing fibers, the chemical and physical features of the interface are critical to the mechanical properties and end use performance of the composite. The compatability between the reinforcing fiber and matrix is then a determining factor in the load sharing ability of the composite. Fiber coatings/binders have been used to enhance the compatability of the reinforcing fibers and resins with which they are to be used. See, for example, U.S. Pat. No. 3,637,417 to Green, hereby incorporated by reference. It is known to utilize silane coupling agents to bond dissimilar materials such as organic polymer and fibrous glass in the field of reinforced plastics. See, e.g., Green, supra, U.S. Pat. No. 4,158,714 to Brichta et al., and U.S. Pat. No. 3,658,748 to Andersen et al., and Marsden and Sterman, HANDBOOK OF ADHESIVES, Second Edition, 40, 640 (1977), all of which are hereby incorporated by reference. It is also known to utilize silane coupling agents to improve fiber to rubber adhesion, as taught by Japanese Kokai Publication J53-024423, hereby incorporated by reference, wherein a polyethylene terephthalate yarn is combined with from 0.7 to 1.2 weight percent on the yarn of a liquid composition consisting essentially of 10 to 30 weight percent of a silane having the structural formula ##STR1## wherein n is 2 to 5, up to one weight percent of a nonionic wetting agent and 70 to 90 weight percent water. The present invention, however, is directed towards reinforcement of plastic composites and not elastomeric structures.
It is also conventional to substitute organic synthetic fibers in whole or in part for glass fibers in reinforced plastics. Some advantages are pointed out in U.S. Pat. No. 3,639,424 to Gray et al., hereby incorporated by reference, wherein heatset polyester staple is used to reinforce thermoplastic/thermosetting polymers for improved impact strength. Heatsetting the fiber allegedly permits uniform fiber dispersion in molded products.
The use of chemically modified polyester fabric as an auxiliary reinforcing agent with glass fibers for thermosets, including polyester, vinyl ester and epoxy, for improved impact resistance and flexural strength over straight glass reinforcement is disclosed in Plastics World Magazine, November, 1980, Volume 38, No. 11, page 102, hereby incorporated by reference.
Japanese Kokai Publication 54-55077 discloses a method for adhesion of polyester fiber/fabric and unsaturated polyester resins through application of a latex, which preferably includes a small quantity of bisphenol epoxy resin, to the polyester fiber/fabric.
The present invention is directed towards improving compatability between a resin matrix and the reinforcing fibers to thereby enhance the reinforced composite properties.